Wireless networking based on the Wi-Fi IEEE 802.11 standards is one of the most widely adopted wireless technologies. An 802.11 network is based on a star topology with two types of wireless devices: clients and access points (APs). Access points (APs) provide an infrastructure function by communicating directly with wireless client devices and linking them to other networks such as the internet.
The 802.11 standards provide service over two frequency bands, 2.4 GHz and 5 GHz. The 2.4 GHz band is approximately 80 MHz in width and allows no more than three non-overlapping channels. The 5 GHz band provides between two and seven times the number of channels and resulting network capacity as the 2.4 GHz band. The 2.4 GHz band is the one most commonly used Wi-Fi devices and hence is the most crowded.
In most countries, however, portions of the 5 GHz band also are used by weather and military radar systems that have priority over Wi-Fi devices. In order to coexist with these critical systems, Wi-Fi radios must comply with Dynamic Frequency Selection (DFS) as defined by an 801.11 specification.
Compliance with DFS is required for both infrastructure (APs) and client devices operating in the 5 GHz band. Infrastructure devices play a larger role in managing DFS, however, as they basically manage the communications sessions with the client devices.
Before transmitting on a DFS channel, an infrastructure device must first listen for the presence of radar signals. If radar is detected, the channel must be vacated and flagged as unavailable. The infrastructure device must continue to monitor for the presence of radar during operation and, if radar is detected, must move to an unoccupied channel and instruct all associated client devices to move also. Client devices are not allowed to transmit on a DFS channel unless instructed by an infrastructure device that the channel is free from radar.
Wi-Fi Direct is an 802.11-defined mechanism that allows a client device to establish a direct communications session (referred to as a Wi-Fi Direct service) with one or more other client devices without the need for an AP. The client device that establishes the Wi-Fi Direct service is said to form a group and, as group owner, manages the peer-to-peer connections with the other devices in the group.